The operation of a semiconductor device is sensitive to its junction temperature. When the junction temperature exceeds its functional limit, semiconductor performance, life, and reliability can be significantly reduced.
In order to increase the operating temperature of a semiconductor device, its components can be configured to increase thermal dissipation. In this way, the device can better dissipate heat so that it can operate at high temperature or so that the area of the final device can be reduced while maintaining the same operating temperature. Since the active region of a semiconductor device is generally confined to its surface and a portion of the starting semiconductor bulk material (e.g. device bulk drift region which is normally thinner than the starting material thickness), there is a large amount of unused material (e.g., on the device's backside) which inhibits heat dissipation. This excess semiconductor bulk material can be removed with semiconductor thinning processes that require dedicated technologies.
In one exemplary manufacturing process, the front side of a semiconductor wafer undergoes semiconductor fabrication processing such that the electronic devices are formed in the front side of the wafer. One or more metallization layers are generally formed on the front side of the wafer to serve as front side electrodes. In the case where the electronic device is a power field effect transistor or an insulated gate bipolar transistor (IGBT), for instance, the control electrode is on the front side of the wafer. In the case of a power diode, the anode is on the front side of the wafer.
After device formation has been performed, including all the diffusion processing steps involved in the formation of the devices, wafer thinning may be performed. Either of two different wafer thinning processes are generally employed.
In a first wafer thinning process, the wafer is flipped over and a central portion of the backside of the wafer is thinned in what is often referred to as the Taiko grinding process. The outer peripheral rim portion of the backside of the wafer is, however, not thinned. As a result, a thicker peripheral edge support portion of the wafer is left surrounding a thinner central portion of the wafer. The thicker peripheral edge support portion provides mechanical stiffening such that the thinner central portion can be handled without cracking of the wafer. The thicker peripheral edge support portion also reduces wafer warpage in later processing steps.
After backside grinding, a backside metallization layer is formed on the thinner central portion of the backside of the wafer. The metallization layer forms an electrode on the backside of the power device. The peripheral edge support portion of the wafer may then be cut off, and the thinner central portion of the wafer may be diced to form individual device dice.
In a second wafer thinning process, sometimes referred to as the temporary bonding process, a semiconductor wafer with a plurality of electronic devices formed on the wafer's front side is bonded to a second wafer (a carrier wafer) by means of an adhesive layer.
The semiconductor wafer is thinned from the wafer backside until a desired target thickness is reached. Based on the semiconductor device type the backside is processed to complete the device structure using, e.g., implantation, thermal processes, metallization, etc. After the device is completed, the carrier wafer is de-bonded from the now thinned semiconductor wafer.
Ongoing improvements in semiconductor device performance are achieved by reducing the device dimensions (device rescaling), which requires further reductions in the semiconductor device thickness in order to optimize the device thermal dissipation.